1. Aim: How do we explain torque?

2. Torque
Torque is the tendency or effectiveness of a force to rotate a body. τ=rFsinф τ=Torque r=position vector F=force Ф= angle between force and position vector

3. Sign of Torque
Torque is positive when it causes counterclockwise rotation. Torque is negative when it causes clockwise rotation.

4. Torque
Torque is a vector quantity
The units of Torque are N m

5. Torque thought questions
Both torque and work are products of force and distance. How are they different?
Torque is a vector and work is a scalar. They are different quantities.
2. If you are trying to loosen a stubborn screw from a piece of wood with a screwdriver and fail, should you find a screwdriver for which the handle is (a) longer or (b) fatter? Why?
A fatter screwdriver will generate more torque because it is a greater distance from the rotation axis.

6. Problem 1
Using torque, how far must person B be from the pivot?

8. Problem 2
Find the net torque about an axis going through O.

10. Problem 3
Which force exerts the greatest torque?

12. The Net Torque on a Cylinder
A one-piece cylinder is shaped as shown below with a core section protruding from the larger drum. The cylinder is free to rotate around the central axis shown in the drawing. A rope wrapped around the drum, of radius R1=1m, exerts a force T1=5N to the right of the cylinder. A rope wrapped around the core of radius R2=0.5m, exerts a force of T2=6N downward on the cylinder. What is the net torque on the cylinder about the rotation axis?
-2.0 N m

13. Net Torque on Cylinder

15. Calculating the net torque
Find the net torque on the wheel shown below about the axle through O if a = 10.0 cm and b = 25.0 cm.

17. Calculating Torque
The fishing pole makes an angle of 20 degrees. What is the torque exerted by the fish about an axis perpendicular to the page and passing through the fisher’s hand?